This invention relates to multiple pane sealed glazing units, particularly to multiple pane units having an insulating, spacing and sealing assembly.
Insulating glass units comprising at least two glass panels separated by a sealed dry air space are widely used in modern building construction for energy conservation to reduce building heat loss through glass surfaces. Sealed insulating glass units generally require spacer means for precisely separating the glass panels. Spacers currently used are generally tubular channels of aluminum or some other metal containing a desiccant to keep the sealed air space dry. The panes of glass are spaced from each other by the metal spacer and adhered to the spacer by a sealing composition applied between each pane and the spacing element. For example, a conventional method of assembling multiple glazing units is to apply a layer or bead of a sealing composition along opposite sides of the spacing element, and then engage the inner surfaces of the glass sheets along the marginal edge. The spacing element is placed between pre-cut glass sheets and the sheets are pressed together to adhere the sheets to the spacing element and to seal the internal air space between the glass sheets from the atmosphere.
The sealant composition is typically a thermoplastic adhesive composition which is applied as a hot melt. In placing the glass sheets to both sides of metal spacer, the sealant composition can be pressed out to such an extent that glass to spacer contact can result. The metal spacers are a much better or cold heat conductor than the surrounding air space and can provide an appreciable path for heat or cold flow. Direct metal-to-glass contact can result in by-passing the gap formed by the space between the panes with undesirable outside-to-inside heat or cold transfer effects. In practice, this effect can manifest itself as a visible line of condensation on the outside of the glass close to its edge, a point which serves to detract from the attractiveness of double glazing to the user. This can also result in a differential dimensional change between the spacer and the glass which can cause stress to develop on the glass and on the seal which can result in damage to and the failure of the solid glass unit.
There have been some attempts to use spacers made of plastic materials, rather than metal. This has, however, been unsuccessful because the sealants which provide relatively reliable bonds between the glass and metal spacers generally do not bond well to plastic spacers. The differential dimensional change that occurs between glass and plastic spacers over a certain range of temperature is much higher than with metal spacers. In addition, most plastics have been found unacceptable for use between glass panes because they can exude volatile materials, such as plasticizers, which could cloud or fog the interior glass surface. The cold flow of the mastic material can also result in penetration of moisture absorbed from the air by the thermoplastic adhesive to penetrate to the space between the pane.